The Turkish Straits System (TSS) is a dangerous and narrow waterway extending between the Black Sea and the Aegean Sea, including the Bosphorus, the Dardanelles, and the Marmara Sea and the Gulf of Izmit. The western banks of the TSS constitute the geographic starting point of the European continent, while the banks to the east are the beginnings of the Asia. TSS is considered one of the most strategically significant waterways of the world. This waterway is the main trading routes linking the Black Sea riparian countries to the world markets. As a result, the density in marine traffic through the TSS has recently reached alarmingly high levels. The aim of this study was to estimate the amount of plastic waste generated aboard merchant ships during their passage through the TSS during the period 2006–2017. This potential resource of waste would potentially impact on the Marmara Sea and its natural environment. The results of this study revealed that merchant ships crossing the TSS generated an average of 187.6 m3 of plastic waste per year. This result suggests that the threat given by the ships crossing this strait is approximately 1% of the total amount of waste recorded in the TSS coastals.